Rubber parts for medical use are known to have possible physical and chemical effects on the quality of preparations depending on the kind of preparation. For example, nitrile butadiene rubber (NBR) and hydrogenated nitrile butadiene rubber (HNBR) are excellent in oil resistance; however, since they are synthesized by emulsion polymerization, an emulsifier, coagulant or other components added in polymerization may be extracted in drugs, particularly causing adverse effects on the drugs. On the other hand, fluorinated rubber, silicone rubber, fluorinated silicone rubber, acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, epichlorohydrin rubber, and butyl-based rubber are excellent in terms of the quality stability of preparations but poor in needle penetration and airtightness.
In this context, a medical rubber stopper is known which includes fluororubber on the liquid-contacting side and butyl rubber laminated to the fluororubber. Such a rubber stopper, however, has the problem of poor productivity because it is prepared by applying an adhesive to a raw material stopper formed of fluororubber, and loading the stopper into a mold for final, molding to laminate the stopper to butyl rubber. Also, a rubber stopper whose liquid-contacting portion is laminated with a fluororesin film has been developed. Such a stopper is prepared by a two-step molding process in which a raw material stopper leg portion (liquid-contacting portion) is first formed and then a final product is formed. Thus, the molding step and the punching step each need to be carried out twice, which disadvantageously creates a complication resulting in poor productivity (Patent Literature 1).